Data storage device synchronizing first channel based on sync mark detected in second channel

ABSTRACT

A data storage device configured to access a magnetic tape is disclosed comprising a plurality of data tracks. A first head is configured to access a first data track comprising a first sync mark, and a second head is configured to access a second data track comprising a second sync mark. The first head is used to read first data from the first data track, wherein the first data comprises a plurality of symbols, and the second head is used to read the second sync mark from the second data track. The first data is symbol synchronized based on the second head reading the second sync mark from the second data track.

BACKGROUND

Conventional tape drive storage systems comprise a magnetic tape woundaround a dual reel (reel-to-reel cartridge) or a single reel (endlesstape cartridge), wherein the reel(s) are rotated in order to move themagnetic tape over one or more transducer heads during write/readoperations. The format of the magnetic tape may be single track ormultiple tracks that are defined linearly, diagonally, or arcuate withrespect to the longitudinal dimension along the length of the tape. Witha linear track format, the heads may remain stationary relative to thelongitudinal dimension of the tape, but may be actuated in a lateraldimension across the width of the tape as the tape moves past the heads.With a diagonal or arcuate track format, the heads may be mounted on arotating drum such that during access operations both the heads and tapeare moved relative to one another (typically in opposite directionsalong the longitudinal dimension of the tape).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a data storage device according to an embodimentcomprising at least one head configured to access a magnetic tape.

FIG. 1B shows an embodiment wherein the data storage device comprises ahead bar comprising a plurality of heads.

FIG. 1C is a flow diagram according to an embodiment wherein first dataread from a first data track is symbol synchronized based on a secondsync mark read from a second data track.

FIG. 1D shows an embodiment wherein the data storage device comprises atape drive assembly configured to access a magnetic tape housed in acartridge assembly.

FIG. 2A shows an embodiment wherein a channel sync block symbolsynchronizes data read from multiple data tracks.

FIG. 2B shows an embodiment wherein the channel sync block comprises async vote block and an offset compensation block.

FIG. 3A shows an embodiment wherein the data read from multiple datatracks is aligned in time.

FIGS. 3B-3D show embodiments wherein the data read from multiple datatracks may be offset in time due, for example, to a longitudinal offsetbetween the heads, a tilt angle of a head bar, and/or a path delay whenthe data is written.

FIG. 4 shows an embodiment wherein the data of multiple data tracks arewritten with a relative path delay in order to avoid a power transientthat may otherwise occur when simultaneously clocking multiple writechannels.

DETAILED DESCRIPTION

FIG. 1A shows a data storage device according to an embodimentcomprising a at least one head 2 _(i) configured to access a magnetictape 4 having a plurality of data tracks. FIG. 1B shows an embodimentwherein a first head 2 ₁ is configured to access a first data track 6 ₁comprising a first sync mark, and a second head 2 ₂ is configured toaccess a second data track 6 ₂ comprising a second sync mark. FIG. 1Cshows an embodiment wherein control circuitry 8 is configured to use thefirst head to read first data from a first data track (block 10),wherein the first data comprises a plurality of symbols, and use thesecond head to read the second sync mark from the second data track(block 12). The first data is symbol synchronized based on the secondhead reading the second sync mark from the second data track (block 14).

In the embodiment of FIG. 1A, the data storage device comprises anembedded magnetic tape 4 installed into a tape drive assembly which, inone embodiment, may be the same form factor as a conventional diskdrive. In another embodiment shown in FIG. 1D, the magnetic tape 4 maybe housed in a cartridge assembly 3 that is inserted into (and ejectedfrom) a tape drive assembly 5 similar to a conventional tape drivemanufactured under the Linear Tape-Open (LTO) standard. In oneembodiment, the tape drive assembly 5 comprises the head 2 configured toaccess the magnetic tape 4, and the control circuitry configured toexecute the flow diagram of FIG. 1B. In the embodiment of FIG. 1D, themagnetic tape 4 is wound around a single reel which may also be employedin the embodiment of FIG. 1A.

In one embodiment, the data written to each data track may be encodedinto symbols of an error correction code (ECC), wherein each symbol maycomprise multiple bits. During a read operation, a sync mark writtenwith the data (e.g., preceding the data) may be read in order to symbolsynchronize the data read from the data track, thereby enabling theerror correction code ECC to decode the data. Conventionally, multiplesync marks may be written with the data (e.g., a primary sync markfollowed by a secondary sync mark) so that if the primary sync mark isunreadable (corrupted), the data read from the data track may still besymbol synchronized by reading the secondary sync mark. However,recording multiple sync marks when writing to a data track reduces thecapacity of the magnetic tape 4 due to the recordable area consumed bythe redundant sync mark(s) as well as the length of each sync markneeded to ensure accurate detection.

In one embodiment, the capacity reduction of writing a secondary syncmark is avoided by instead detecting a sync mark of a second readchannel in order to symbol synchronize the data of a first read channel.FIG. 2A shows an example of this embodiment wherein while a plurality ofheads 2 ₁-2 _(N) concurrently read a plurality of data tracks the readdata 16 ₁-16 _(N) are processed by respective sync mark detectors 18₁-18 _(N). A channel sync block 20 evaluates the outputs of the syncmark detectors 18 ₁-18 _(N) in order to symbol synchronize a datadetector 22 ₁-22 _(N) of each read channel. In one embodiment when thesync mark of a first read channel is corrupted, the data detector of thefirst read channel is symbol synchronized based on reading the sync markof a second read channel, thereby obviating the need to write asecondary sync mark in each data track. For example, when the channelsync block 20 of FIG. 2A determines the first sync mark detector 18 ₁has missed the corresponding sync mark written on the first data track,the channel sync block 20 may symbol synchronize the first data detector22 ₁ based on when the second sync mark detector 18 ₂ detects thecorresponding sync mark written in the second data track. In oneembodiment, the channel sync block 20 may symbol synchronize a datadetector of a first read channel based on detecting the sync mark of anadjacent, second read channel. That is, in one embodiment a first readchannel may be symbol synchronized using an adjacent read channel due tothere being a tighter timing tolerance between adjacent read channels.In another embodiment, a first read channel may be symbol synchronizedbased on any one of the other read channels that successfully detectsthe respective sync mark.

In one embodiment, the channel sync block 20 of FIG. 2A may symbolsynchronize at least some of the data detectors 22 ₁-22 _(N) when thesync mark of any one of the read channels is detected. In anotherembodiment, the channel sync block 20 may symbol synchronize at leastsome of the data detectors 22 ₁-22 _(N) when M of N of the sync marks ofthe read channels have been detected. For example in an embodimentemploying eight heads, the channel sync block 20 may symbol synchronizeat least some of the data detectors 22 ₁-22 _(N) when, for example, anyfour of the eight sync marks of the eight read channels have beendetected. FIG. 2B shows an example of this embodiment wherein thechannel sync block 20 comprises a sync vote block 24 configured toprocess the outputs of the sync mark detectors 18 ₁-18 _(N) to determinewhen a sufficient number of the sync marks have been detected. In oneembodiment, symbol synchronizing at least some of the data detectors 22₁-22 _(N) based on detecting M of N sync marks of multiple read channelsenables writing shorter sync marks in each data track since symbolsynchronizing the read channels based on multiple sync marks is similarto writing multiple consecutive sync marks to a single data track.Accordingly this embodiment may increase the capacity of the magnetictape 4 by obviating secondary sync marks in each data track, as well asby reducing the length of each sync mark written to each data track.

In the embodiment of FIG. 2B, the channel sync block 20 comprises anoffset compensation block 26 configured to compensate for a phase offsetbetween the heads 2 ₁-2 _(N). That is, when there is a relative phaseoffset between the data read from each data track, the offsetcompensation block 26 compensates for the phase offset between the readchannels when reading the multiple data tracks in order to correctlysymbol synchronize at least some of the data detectors 22 ₁-22 _(N).

FIG. 3A shows an example where all of the read channels (eight in thisexample) are aligned in time during a read operation such that there isno need to compensate for a phase offset between the read channels. Thatis in this example, all of the data detectors 22 ₁-22 _(N) of FIG. 2Bmay be symbol synchronized relative to a common time reference duringthe read operation, whereas in the examples of FIGS. 3B and 3C there maybe a phase offset between the read channels. For example in theembodiment of FIG. 1B, a head bar 28 comprising the plurality of heads 2₁-2 _(N) may be tilted (e.g., relative to a center pivot point) in orderto compensate for a distortion of the magnetic tape 4 (e.g., acontraction or expansion). However when reading the data tracks 6 ₁-6_(N), tilting the head bar 28 at an angle different than when writingthe data tracks 6 ₁-6 _(N) results in a phase offset between the readchannels such shown in FIG. 3B or 3C. FIG. 3D shows an embodimentwherein a phase offset between the read channels may be due to anarbitrary longitudinal offset between the heads 2 ₁-2 _(N) when mountedor fabricated on the head bar 28. FIG. 4 shows an embodiment whereinwhen writing the data tracks 6 ₁-6 _(N), the write data 30 ₁-30 _(N) maybe delayed within each write channel by a predetermined path delay 32₁-32 _(N) so as to avoid a power transient that may otherwise occur dueto simultaneously clocking the write channels. In this embodiment, thepath delays 32 ₁-32 _(N) during the write operation results in a phaseoffset between the read channels during a read operation, such as shownin FIG. 3B or 3C. Accordingly when symbol synchronizing the datadetectors 22 ₁-22 _(N) during a read operation, the offset compensationblock 26 of FIG. 2B compensates for a phase offset between the readchannels due, for example, to a longitudinal offset of the heads,tilting the head bar, path delays during the write operation, etc.

Any suitable technique may be employed to determine the phase offsetbetween the read channels during a read operation. In an embodimentemploying path delays during the write operation such as shown in FIG.4, the phase offset between the read channels may be configured based onthe predetermined path delays. In another embodiment, the phase offsetbetween the read channels may be measured during a calibrationprocedure. For example, a test pattern may be written to the data tracks6 ₁-6 _(N) which are then read in order to measure the phase offsetbetween the read channels (e.g., based on when each sync mark in eachdata track is detected). In one embodiment, the phase offset between theread channel may be measured for different tilt angles of the head bar,that is, at tilt angles that represent a delta between writing andreading the test pattern.

In another embodiment, the phase offset between the read channels may bemeasured and updated prior to and/or during a read operation. Forexample, prior to reading a target segment of the data tracks the datatracks may be read in order to read the sync marks in each data trackand measure the current phase offset between the read channels (e.g., atthe current tilt angle of the head bar 28) based on the relative timingwhen each sync marks is detected. Similarly when reading the targetsegment of the data tracks, the phase offset between the read channelsmay be measured and updated each time a sync mark is successfullydetected. When a sync mark is missed (e.g., due to being corrupted), thephase offset for the corresponding read channel is not updated.

In one embodiment, the control circuitry 8 may employ sufficientbuffering of the read data when the sync mark of a read channel ismissed. For example, when the channel sync block 20 of FIG. 2Adetermines the sync mark has been missed for a particular data track,the channel sync block 20 may buffer read data for the correspondingdata detector. When M of N sync marks from the other read channels aresuccessfully detected, the channel sync block 20 symbol synchronizes thebuffered read data and enables the corresponding data detector(s).

In one embodiment, the sync mark may be written with the same pattern ofmagnetic transitions in each of the data tracks, wherein the sync markmay be detected by correlating read data with the target sync markpattern. In another embodiment, the sync mark written to a first datatrack may comprise a first pattern of magnetic transitions and the syncmark written to a second data track may comprise a second pattern ofmagnetic transitions different from the first pattern. For example, inone embodiment each sync mark of the multiple data tracks may beconsidered as segments of a concatenated sync mark pattern. In thisembodiment, writing different sync mark patterns in at least two datatracks enables the concatenated sync mark pattern to attain anydesirable characteristic, such as increasing the propensity for accuratedetection. In another embodiment, one of multiple possible sync markpatterns may be written to a data track wherein each sync mark detector18 ₁-18 _(N) of FIG. 2A may concurrently search for all possible syncmark patterns. For example, in one embodiment any suitable data (e.g.,servo data) may be encoded by modulating different sync mark patternsacross the data tracks. In an embodiment wherein one of two sync markpatterns may be written to each data track, the data may be binaryencoded wherein a “0” bit may be represented by a first sync markpattern and a “1” bit may be represented by a second sync mark pattern.In this manner, the concatenated sync marks may represent a multi-bitdigital value (e.g., an 8-bit value when writing 8 data tracks such asshown in FIG. 3A).

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a data storage controller, orcertain operations described above may be performed by a read channeland others by a data storage controller. In one embodiment, the readchannel and data storage controller are implemented as separateintegrated circuits, and in an alternative embodiment they arefabricated into a single integrated circuit or system on a chip (SOC).In addition, the control circuitry may include a suitable preamp circuitimplemented as a separate integrated circuit, integrated into the readchannel or data storage controller circuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry. In someembodiments, at least some of the flow diagram blocks may be implementedusing analog circuitry (e.g., analog comparators, timers, etc.), and inother embodiments at least some of the blocks may be implemented usingdigital circuitry or a combination of analog/digital circuitry.

In addition, any suitable electronic device, such as computing devices,data server devices, media content storage devices, etc. may comprisethe storage media and/or control circuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device configured to access amagnetic tape comprising a plurality of data tracks, the data storagedevice comprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; and control circuitryconfigured to: use the first head to read first data from the first datatrack, wherein the first data comprises a plurality of symbols; use thesecond head to read the second sync mark from the second data track; andwhen the first sync mark is corrupted, symbol synchronize the first databased on the second head reading the second sync mark from the seconddata track.
 2. The data storage device as recited in claim 1, wherein:the first sync mark comprises a first pattern of magnetic transitions;the second sync mark comprises a second pattern of magnetic transitions;and the first pattern is the same as the second pattern.
 3. The datastorage device as recited in claim 1, wherein: the first sync markcomprises a first pattern of magnetic transitions; the second sync markcomprises a second pattern of magnetic transitions; and the firstpattern is different from the second pattern.
 4. A data storage deviceconfigured to access a magnetic tape comprising a plurality of datatracks, the data storage device comprising: a first head configured toaccess a first data track comprising a first sync mark; a second headconfigured to access a second data track comprising a second sync mark;and control circuitry configured to: use the first head to read firstdata from the first data track, wherein the first data comprises aplurality of symbols; detect the first sync mark when reading the firstdata track; use the second head to read the second sync mark from thesecond data track; symbol synchronize the first data based on the secondhead reading the second sync mark from the second data track; symbolsynchronize the first data when the first sync mark is detected; andwhen the first sync mark is not detected, symbol synchronize the firstdata based on the second head reading the second sync mark from thesecond data track.
 5. A data storage device configured to access amagnetic tape comprising a plurality of data tracks, the data storagedevice comprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; and control circuitryconfigured to: use the first head to read first data from the first datatrack, wherein the first data comprises a plurality of symbols; use thesecond head to read the second sync mark from the second data track;symbol synchronize the first data based on the second head reading thesecond sync mark from the second data track; measure a phase offsetbetween the first head and the second head; and symbol synchronize thefirst data based on the second head reading the second sync mark fromthe second data track and based on the measured phase offset between thefirst head and the second head.
 6. The data storage device as recited inclaim 5, further comprising a head bar comprising the first head and thesecond head, wherein the control circuitry is further configured to:tilt the head bar at an angle to compensate for a distortion of themagnetic tape; and measure the phase offset between the first head andthe second head for a plurality of different tilt angles.
 7. A datastorage device configured to access a magnetic tape comprising aplurality of data tracks, the data storage device comprising: a firsthead configured to access a first data track comprising a first syncmark; a second head configured to access a second data track comprisinga second sync mark; and control circuitry configured to: use the firsthead to read first data from the first data track, wherein the firstdata comprises a plurality of symbols; use the second head to read thesecond sync mark from the second data track; symbol synchronize thefirst data based on the second head reading the second sync mark fromthe second data track; use the first head to first write the first datato the first data track; use the second head to second write the seconddata to the second data track, wherein the second write is delayedrelative to the first write by a predetermined path delay; and symbolsynchronize the first data based on the second head reading the secondsync mark from the second data track and based on the predetermined pathdelay.
 8. A data storage device configured to access a magnetic tapecomprising a plurality of data tracks, the data storage devicecomprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; a third head configuredto access a third data track comprising a third sync mark; and controlcircuitry configured to: use the first head to read first data from thefirst data track, wherein the first data comprises a plurality ofsymbols; use the second head to read second data from the second datatrack, wherein the second data comprises a plurality of symbols; use thethird head to read third data from the third data track, wherein thethird data comprises a plurality of symbols; and when the first syncmark is corrupted, symbol synchronize the first data, the second data,and the third data when at least one of the first sync mark, the secondsync mark, or the third sync mark is detected.
 9. The data storagedevice as recited in claim 8, wherein: the first sync mark comprises afirst pattern of magnetic transitions; the second sync mark comprises asecond pattern of magnetic transitions; and the first pattern is thesame as the second pattern.
 10. The data storage device as recited inclaim 8, wherein: the first sync mark comprises a first pattern ofmagnetic transitions; the second sync mark comprises a second pattern ofmagnetic transitions; and the first pattern is different from the secondpattern.
 11. A data storage device configured to access a magnetic tapecomprising a plurality of data tracks, the data storage devicecomprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; a third head configuredto access a third data track comprising a third sync mark; and controlcircuitry configured to: use the first head to read first data from thefirst data track, wherein the first data comprises a plurality ofsymbols; use the second head to read second data from the second datatrack, wherein the second data comprises a plurality of symbols; use thethird head to read third data from the third data track, wherein thethird data comprises a plurality of symbols; symbol synchronize thefirst data, the second data, and the third data when at least one of thefirst sync mark, the second sync mark, or the third sync mark isdetected; and symbol synchronize the first data, the second data, andthe third data when at least two of the first sync mark, the second syncmark, or the third sync mark is detected.
 12. A data storage deviceconfigured to access a magnetic tape comprising a plurality of datatracks, the data storage device comprising: a first head configured toaccess a first data track comprising a first sync mark; a second headconfigured to access a second data track comprising a second sync mark;a third head configured to access a third data track comprising a thirdsync mark; and control circuitry configured to: use the first head toread first data from the first data track, wherein the first datacomprises a plurality of symbols; use the second head to read seconddata from the second data track, wherein the second data comprises aplurality of symbols; use the third head to read third data from thethird data track, wherein the third data comprises a plurality ofsymbols; symbol synchronize the first data, the second data, and thethird data when at least one of the first sync mark, the second syncmark, or the third sync mark is detected; measure a phase offset betweenthe heads; and symbol synchronize the first data, the second data, andthe third data based on measured phase offset between the heads.
 13. Thedata storage device as recited in claim 12, further comprising a headbar comprising the first head, the second head, and the third head,wherein the control circuitry is further configured to: tilt the headbar at an angle to compensate for a distortion of the magnetic tape; andmeasure the phase offset between the heads for a plurality of differenttilt angles.
 14. A data storage device configured to access a magnetictape comprising a plurality of data tracks, the data storage devicecomprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; a third head configuredto access a third data track comprising a third sync mark; and controlcircuitry configured to: use the first head to read first data from thefirst data track, wherein the first data comprises a plurality ofsymbols; use the second head to read second data from the second datatrack, wherein the second data comprises a plurality of symbols; use thethird head to read third data from the third data track, wherein thethird data comprises a plurality of symbols; symbol synchronize thefirst data, the second data, and the third data when at least one of thefirst sync mark, the second sync mark, or the third sync mark isdetected; use the first head to first write the first data to the firstdata track; use the second head to second write the second data to thesecond data track, wherein the second write is delayed relative to thefirst write by a first predetermined path delay; use the third head tothird write the third data to the third data track, wherein the thirdwrite is delayed relative to the first write by a second predeterminedpath delay; and symbol synchronize the first data, the second data, andthe third data based on the first and second path delays.
 15. A datastorage device configured to access a magnetic tape comprising aplurality of data tracks, the data storage device comprising: a firsthead configured to access a first data track comprising a first syncmark; a second head configured to access a second data track comprisinga second sync mark; a means for using the first head to read first datafrom the first data track, wherein the first data comprises a pluralityof symbols; a means for using the second head to read the second syncmark from the second data track; and a means for symbol synchronizingthe first data based on the second head reading the second sync markfrom the second data track when the first sync mark is corrupted. 16.The data storage device as recited in claim 15, wherein: the first syncmark comprises a first pattern of magnetic transitions; the second syncmark comprises a second pattern of magnetic transitions; and the firstpattern is the same as the second pattern.
 17. The data storage deviceas recited in claim 15, wherein: the first sync mark comprises a firstpattern of magnetic transitions; the second sync mark comprises a secondpattern of magnetic transitions; and the first pattern is different fromthe second pattern.
 18. A data storage device configured to access amagnetic tape comprising a plurality of data tracks, the data storagedevice comprising: a first head configured to access a first data trackcomprising a first sync mark; a second head configured to access asecond data track comprising a second sync mark; a means for using thefirst head to read first data from the first data track, wherein thefirst data comprises a plurality of symbols; a means for detecting thefirst sync mark when reading the first data track; a means for using thesecond head to read the second sync mark from the second data track; ameans for symbol synchronizing the first data based on the second headreading the second sync mark from the second data track; a means forsymbol synchronizing the first data when the first sync mark isdetected; and when the first sync mark is not detected, a means forsymbol synchronize the first data based on the second head reading thesecond sync mark from the second data track.
 19. A data storage deviceconfigured to access a magnetic tape comprising a plurality of datatracks, the data storage device comprising: a first head configured toaccess a first data track comprising a first sync mark; a second headconfigured to access a second data track comprising a second sync mark;a means for using the first head to read first data from the first datatrack, wherein the first data comprises a plurality of symbols; a meansfor using the second head to read the second sync mark from the seconddata track; a means for symbol synchronizing the first data based on thesecond head reading the second sync mark from the second data track; ameans for measuring a phase offset between the first head and the secondhead; and a means for symbol synchronizing the first data based on thesecond head reading the second sync mark from the second data track andbased on the measured phase offset between the first head and the secondhead.
 20. The data storage device as recited in claim 19, furthercomprising: a head bar comprising the first head and the second head; ameans for tilting the head bar at an angle to compensate for adistortion of the magnetic tape; and a means for measuring the phaseoffset between the first head and the second head for a plurality ofdifferent tilt angles.